Suppression of ovarian progesterone production in dairy cows using an implant of GnRH-agonist (deslorelin) for the purpose of evaluating

Objective To evaluate the potential of an implant of a GnRH-agonist (deslor elin) to create a progesterone free animal suitable for studying progestero ne (P4) metabolism in intact cows by measuring blood P4 and faecal P4 metab olites. Methods Experiment 1: Eighteen non-lactating cycling Holstein-Friesian cows , 4 to 7 years old, were allocated to one of three groups to study plasma P 4 concentrations preceding an intravaginal insert. These groups comprised: i) a deslorelin group (GnRH-agonist implanted); ii) a PGF group receiving t wo injections of prostaglandin (PGF(2 alpha)) 12 days apart; and, iii) an o variectomised (OVX) group. An intravaginal device (CIDR) was inserted into the vagina of each animal and left in place for 11 days. Plasma P4 concentr ations were measured during the study period. Experiment 2: Twelve non-lactating cycling Holstein-Friesian cows, 4 to 7 y ears old, were allocated to two groups: i) a deslorelin group (GnRH-agonist implanted); and ii) an ovariectomised group. Plasma P4 and faecal P4 metab olites (20-oxo-pregnanes, 20 alpha -OH and 20 beta -OH) were monitored for a period of 5 weeks. Results Experiment 1: Average plasma P4 concentration did not differ betwee n the three groups (1.28, 1.43 and 1.55 ng/mL for deslorelin, OVX and PGF c ows, respectively, P=0.8) during the period of supplementation. Experiment 2: There was no difference in plasma P4 (mean plasma P4<0.02 ng/ mL, P=0.9) and faecal P4 metabolites between deslorelin and OVX cows 2 week s after the implantation (P=0.7). Conclusions These data showed that a GnRH-agonist (deslorelin) implant may be used as an alternative to ovariectomy to create a progesterone free anim al suitable for studying the metabolism of administered P4.